(1) Field of the Invention
The present invention relates to the field of nuclear medicine systems. Specifically, the present invention relates to signal processing systems for scintillation detectors.
(2) Prior Art
Gamma cameras performing Single Photon Emission Computed Tomography (SPECT) have been utilized in nuclear medicine for some time. Anger proposed and developed such a system in the 1950s which has been modified and improved extensively with the introduction of high speed digital computer systems for image acquisition as well as image reproduction. However, SPECT camera systems utilize a collimator that is installed in front of the scintillation crystal within a scintillation detector. The collimator is used to collimate the incoming gamma rays so that only rays of a certain angle of incidence actually penetrate the crystal. Although SPECT imaging is extensively used in nuclear medicine and provides beneficial image quality, the collimator introduces a source of image degradation in nuclear medicine images and tends to somewhat reduce the resolution and quality of images acquired by SPECT systems.
Cameras performing Positron Emission Tomography (PET) have been utilized in nuclear medicine as well with the introduction of relatively high speed detection electronics and computer systems for image acquisition and processing. These PET camera systems utilize a form of the scintillation detector that is used in SPECT systems, however, they do not utilize a collimator. In PET systems, the detection of two gamma rays in coincidence (in different scintillation detectors) is used to compute imaging information. A PET system employing two scintillation detectors is described in a paper presented by Gerd Muehllehner, M. P. Buchin, and J. H. Dudek entitled "Performance Parameters of a Positron Imaging Camera," published in the IEEE Transactions on Nuclear Science, Volume NS-23, No. 1, on February 1976 and also in a paper entitled "Performance Parameters of a Longitudinal Tomographic Positron Imaging System" by Paans, deGraaf, Welleweerd, Vaalburg and Woldring, in Nuclear Instruments and Methods, Volume 192, Nos 2, 3, on Feb. 1, 1982 pages 491-500. By utilizing higher energy gamma rays and eliminating the collimators, PET systems offer greatly improved image resolution and image quality over SPECT systems. Because the collimators are removed in PET systems, the detected count rate is higher in PET cameras over SPECT camera systems. Although both camera systems utilize different detection electronics and other circuitry, both PET and SPECT systems employ scintillation detectors.
The detection hardware for SPECT and PET systems is different in terms of the manner in which the systems detect and record events and is also different because PET systems operate at higher count rates over SPECT systems. Further, SPECT systems employ a different radionuclide over PET systems and detect gamma rays at different energy levels over PET systems. For this reason, although SPECT and PET systems are versatile and useful within nuclear medicine, in the prior art, different camera systems have been implemented and supplied for PET and SPECT imaging. Therefore, a facility desiring to perform SPECT and PET imaging is required to acquire two separate camera systems at a relatively greater expense.
It would be advantageous, then, to provide a nuclear camera system offering the ability to perform both SPECT and PET imaging techniques within a single configurable system. Therefore, the expense of acquiring two separate systems can be advantageously avoided. The present invention offers such advantageous capabilities.
Accordingly, it is an object of the present invention to provide a single dual head nuclear camera system that is switchable between SPECT imaging and PET imaging to perform either mode of operation. It is an object of the present invention to provide such a system employing high count rate event detection circuitry for PET studies and also switchable to offer detection of gamma rays of different energy distributions, one for SPECT imaging and one for PET imaging. It is also an object of the present invention to provide a scintillation detector pair having switchable triggering capabilities that can be used to detect and record SPECT events and also switched to perform coincidence detection for PET imaging. It is yet another object of the present invention to employ zonal triggering capabilities for event detection in both SPECT or PET imaging modes. These and other objects of the present invention not specifically recited will become clear within discussions of the present invention herein.